By Robert Hazen, George Mason University
In 1977, Jack Corliss, an oceanographer at the University of Oregon, was engaged in a whole series of deep dives. While studying the ridge systems and their volcanoes, he discovered deep spectacular ecosystems: new species of clams and crabs, shrimp, giant six-foot-long tubeworms that are blood-red. And yet, these deep ecosystems were dominated by one life form above all else—microbes. It was the finding of these microbes that strengthened his hydrothermal origin-of-life hypothesis. How?
Microbes are exceptional for at least three reasons. First of all, they are largely independent of the surface. They don’t use the Sun’s energy in any way. Rather, they obtain their energy by oxidizing or reducing minerals that spew out of the hydrothermal vents. They gain energy through oxidation-reduction reactions, essentially using the chemical energy of the Earth, produced by the Earth’s heat.
The second remarkable feature is that these microbes require high pressure. For them, high pressures and high temperatures are not an extreme environment; they’re the normal environment of life. The third remarkable feature is that genetic studies show that microbes are among the most primitive life forms on Earth. They’re closer, genetically, to the oldest common ancestor than almost anything we see on the surface of the Earth.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
The Hydrothermal Origin-of-life
Subsequent studies went on to show that microbes thrived in many of these places underground where there were rock and water. Indeed, if we drill a hole where we’re standing right now, about a mile or two straight down, chances are that if we brought up that rock core and looked at it carefully, there would be life forms living in the rock. Any place where rock and water interact, such as the submarine hot springs, there are likely to be microbes. This is because rocks turn out to be a good source of food for these microbes.
Deep life is sparse, but the volume of the Earth’s crust is immense, in the order of a billion cubic kilometers. It’s possible that the total mass of these tiny microbes is comparable to all the animals and plants, all the trees that we see on the Earth’s surface. Thus, it’s reasonable to assume that the Earth’s biomass may indeed be dominated by microbes living on rock.
In addition to this, there are some other reasons to consider Corliss’s hydrothermal hypothesis, and these reasons come from geology.
The Nebular Hypothesis
The nebular hypothesis proposes that the Sun, the Earth, and the other planets formed from a vast cloud of dust and gas. There was a great bombardment, in which all these materials came together by gravity, and then we had volcanoes that formed the ocean and the atmospheres. In the late stage of the Earth’s formation, any large impact would’ve come in, smashed the Earth’s surface, and basically blown away the atmosphere as well as, the ocean. Hence, the entire surface of the Earth would’ve been, most probably, sterilized, time and time again.
However, if life arose in a deep hydrothermal zone, those microbes—living in rock deep beneath the surface—would be much more insulated from these insults, and therefore, it’s very likely that deep life could’ve survived when surface life could not have.
Another reason for studying the hydrothermal origin comes from planetary science, and this is more a wish than a reason. It’s because many planetary scientists have now realized the existence of other hydrothermal zones on other planets and moons. Earth is the only known world with a surface ocean. But Mars must have had surface water early in its history, and it’s very likely that Mars now has subsurface water and subsurface hydrothermal systems that still exist.
NASA and Deep-ocean Research
So, if life was to arise at the interface between an ocean and atmosphere, we’re really restricted to the Earth ,and possibly Mars, early in its history. However, if life can originate in a deep hydrothermal zone, we can include the deep interior of Mars, as well as Europa, which is one of the moons of Jupiter; Callisto, another one of the moons of Jupiter; Titan, a moon of Saturn; and perhaps other bodies in the solar system as well. Along with many others, these are all where water is believed to exist in a liquid state beneath the surface of planets and moons.
NASA is now planning missions to Europa, which is the most likely site for this. Europa, it turns out, has a deep ocean beneath a thin crust, which is basically an ice surface crust over the entire moon. Understandably, NASA is studying the developments made in deep-ocean research on Earth, the reason being that if we can develop probes for the deep ocean on Earth, it’s possible that we can send a spacecraft to Europa and probe Europa’s deep ocean.
Hence, we can, potentially, look for life and other geological phenomena in Europa. NASA has now extended its support to oceanographic research. Interestingly, it does seem a bit amusing that when we look up into the heavens, we actually can make our plans by going deep under the oceans of Earth.
Common Questions about the Hydrothermal Origin-of-life Hypothesis
Genetic studies show that microbes are among the most primitive life forms on Earth. They’re closer, genetically, to the oldest common ancestor than almost anything we see on the surface of the Earth.
If life can originate in a deep hydrothermal zone, we can include the deep interior of Mars, as well as Europa, which is one of the moons of Jupiter; Callisto, another one of the moons of Jupiter; Titan, a moon of Saturn; and perhaps other bodies in the solar system as well.
NASA is studying the developments made in deep-ocean research on Earth, the reason being that if we can develop probes for the deep ocean on Earth, it’s possible that we can send a spacecraft to Europa and probe Europa’s deep ocean.